Polar and Non-polar molecules Watch

Neuron13
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Someone please explain polar and non-polar molecules and bonds to me. It just doesn't make sense. Detail and simplicity would be much appreciated
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alow
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Due to their electronic configurations and nuclear charges, elements attract electrons to differing degrees. Therefore when two different elements bond, one side of the molecule will have more electron density than the other.
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Neuron13
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(Original post by alow)
Due to their electronic configurations...
Can you give me an example?
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alow
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(Original post by Neuron13)
Can you give me an example?
Sure.

An example to illustrate the point would be hydrogen chloride, HCl. With the structure H-Cl.

Chlorine is more electronegative (attracts electrons more) than hydrogen, so the molecule will be slightly negatively charged on the chlorine side, and slightly positively charged on the hydrogen side. Therefore the molecule is polar.
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1256601
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It's got to do with the spread of dipoles, carbon monoxide and carbon dioxide are good examples. The C-O bond is polar, so CO is a polar molecule as there is only one dipole. CO2 is non polar despite having polar bonds as the dipoles are symmetrical and therefore cancel each other out, hope i've helped

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Neuron13
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(Original post by alow)
Sure.

An example to illustrate the point would be hydrogen chloride, HCl. With the structure H-Cl.

Chlorine is more electronegative (attracts electrons more) than hydrogen, so the molecule will be slightly negatively charged on the chlorine side, and slightly positively charged on the hydrogen side. Therefore the molecule is polar.
Ok so, if it is charged, it is polar; in the sense it has a positive and negative pole
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alow
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(Original post by Neuron13)
Ok so, if it is charged, it is polar; in the sense it has a positive and negative pole
Yeah, that's what it means. And because there are two poles we call it a dipole.
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MexicanKeith
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(Original post by Neuron13)
Ok so, if it is charged, it is polar; in the sense it has a positive and negative pole
H-Cl certainly has a positive (H) and negative (Cl) pole. Be careful with saying it is charged though, the overall molecule has no charge (ie it isn't an ion).
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Neuron13
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(Original post by alow)
Yeah, that's what it means. And because there are two poles we call it a dipole.
Jeez. I have been enlightened. Thank you
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alow
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(Original post by Neuron13)
Jeez. I have been enlightened. Thank you
No worries.

The only other thing you really have to worry about is molecules which have polar bonds which aren't polar overall.

To give an example of this, think of CF4. This molecule has the same structure as methane, just replace the hydrogens with fluorines. So Fluorine is the most electronegative element, meaning the fluorine side of each C-F bond will be negatively charged. However, as the fluorines surround the carbon, there is no overall dipole as the molecule is equally negatively charged on all sides.

You can think of it as a vector addition of dipoles, if that helps. In CF4 each of the dipole vectors has an equal vector pointing in the opposite direction so there is zero overall dipole.
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K-Man_PhysCheM
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(Original post by Neuron13)
Ok so, if it is charged, it is polar; in the sense it has a positive and negative pole
'Charged' isn't really the best word. The ammonium ion, NH4+, is positively charged because the whole molecule has one more proton than it has electrons. The difference in electronegativity between Nitrogen and Hydrogen is such that the N-H bond is polar, but the whole ammonium ion is non-polar because of its symmetrical 3-D shape that cancels out the poles from the polar bonds. But it is definitely charged.

But if there are poles in the molecule which do not cancel out, then the molecule is polar.

Polar covalent bonds form if there is enough difference in electronegativity (or electron-pulling strength) between two atoms which are covalently bonded together. For example, CO has polar covalent bonding as oxygen is more electronegative than carbon, so it attracts more electrons and there is a slightly higher electron density around the oxygen. The whole molecule is polar (but NOT charged).

On the other hand, CO2 (O=C=O) has two polar bonds, but as the molecule is symmetrical, the poles 'cancel out', and so overall, the molecule is non-polar, despite the fact that it contains two polar covalent (double) bonds.
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Neuron13
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(Original post by K-Man_PhysCheM)
...
Ok so... it depends upon electronegativity and in a way, the symmetry of the bonds??
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K-Man_PhysCheM
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(Original post by Neuron13)
Ok so... it depends upon electronegativity and in a way, the symmetry of the bonds??
The polar or non-polar nature of covalent bonds depends on the difference in electronegativity between the two bonding atoms.

The polar or non-polar nature of a whole molecule depends on the symmetry of the polar covalent bonds in a molecule.
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charco
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(Original post by K-Man_PhysCheM)
'Charged' isn't really the best word. The ammonium ion, NH4+, is positively charged because the whole molecule has one more proton than it has electrons, but (off the top of my head) the difference in electronegativity between Nitrogen and Hydrogen is so small that the ammonium ion is non-polar (and also it's symmetrical 3-D shape would make any polar bonds cancel out anyway, so even if N-H bonds were polar, the whole molecule itself would not be polar. But it is definitely charged.

But if there are poles in the molecule which do not cancel out, then the molecule is polar.

Polar covalent bonds form if there is enough difference in electronegativity (or electron-pulling strength) between two atoms which are covalently bonded together. For example, CO has polar covalent bonding as oxygen is more electronegative than carbon, so it attracts more electrons and there is a slightly higher electron density around the oxygen. The whole molecule is polar (but NOT charged).

On the other hand, CO2 (O=C=O) has two polar bonds, but as the molecule is symmetrical, the poles 'cancel out', and so overall, the molecule is non-polar, despite the fact that it contains two polar covalent (double) bonds.
Nitrogen and hydrogen have very different electronegativities. The N-H bond is polar.
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K-Man_PhysCheM
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(Original post by charco)
Nitrogen and hydrogen have very different electronegativities. The N-H bond is polar.
Indeed, sorry, will edit.
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Kallisto
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(Original post by Neuron13)
Ok so... it depends upon electronegativity and in a way, the symmetry of the bonds??
Don't know whether it was mentioned by other members before, but as a rule non-polar bonds are existed when the attraction between atoms for creating a bond to each other is weak. In terms of the electronegativity difference, it is between 0 to 0.4. In this intervall of the difference, the attraction is (quite) weak and that is why the bonds are regarded as non-polar. Above 0.4, the bonds are regarded as polar, as the attractions are getting stronger. *
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